1. Field of the Invention
The present invention relates to the construction of a contact portion of a vibrating member or a moving member for use in a vibration wave driving device, and to a method of processing this contact portion.
2. Related Background Art
A vibration wave motor, which is a vibration wave driving device, has a vibrating member generating vibration serving as a drive source, and this vibrating member is composed of an elastic member and a piezoelectric element serving an electro-mechanical energy conversion element. A piezoelectric element has two drive phases that have a phase shift of, for example, 90 degrees. When drive signals (alternating signals) having a phase shift of 90 degrees are applied to these two drive phases, a vibration which is a traveling wave is generated wave is generated on the surface of the elastic member. When a rotor is brought into press contact with this elastic member, the rotor is driven by the traveling wave generated on the surface of the elastic member.
Conventional well-known vibration wave motors of the type in which a rotor is rotated are annular, disc-like, or bar-like configurations. In the following, the construction of a bar-like vibration wave motor will be described.
FIG. 12 is a sectional view of an example of a conventional bar-like vibration wave motor. A vibrating member 1 generating vibration is constructed of elastic members 9 and 10 formed of metal or the like; a frictional ring 9b attached to the forward end surface of the elastic member 9 by adhesion, brazing or the like and formed, for example, of alumina ceramics; and a laminated piezoelectric element 11 held between the elastic members 9 and 10 and serving as a layered electromechanical energy conversion element.
After attaching the frictional ring 9b to the elastic member 9, the surface of the frictional ring 9b which is on the opposite side of the attachment surface, that is, the frictional surface, is polished to enhance its flatness and to smoothen its surface.
At the center of the elastic member 9, the piezoelectric element 11, and the elastic member 10, there is formed a through-hole, into which a support bar 5 constituting a framework member of the motor is inserted. One end portion of the support bar 5 protrudes beyond the elastic member 10, and a nut 6 is engaged with a screw portion 5b formed on the protruding portion. The support bar 5 has a large diameter portion 5a in contact with a step formed on the inner side of the elastic member 9. By fastening the nut 6, the elastic member 9, the laminated piezoelectric element 11 and the elastic member 10, which are held between the large diameter portion 5a and the nut 6, are pressed against each other and secured in position.
Reference numeral 2 indicates a rotor (moving member) arranged opposite the forward end surface of the elastic member 9. It is composed of a cylindrical main body 21 and a contact spring 22 fitted onto the outer periphery of the main body 21, and both components are joined together by adhesion, welding or the like. The rotor 2 is engaged with an output gear 4 rotating integrally with the rotor 2; this gear 4 slides on a motor mounting flange 7 through the intermediation of lubricating oil. A screw portion 5c at the other end of the support bar 5 is fixed to the flange 7, and the vibrating member 1 is supported by fixing the flange 7 to a bottom board (not shown) by means of a screw. On the inner wall of the through-hole at the center of the main body 21 of the rotor 2, there is formed a step constituting a spring seat portion 21a, and a pressure spring 8 is arranged between the spring seat portion 21a and the output gear 4, the contact spring 22 of the rotor 2 being brought into press contact with the frictional ring 9b of the vibrating member 1.
The driving principle of the vibration wave motor of FIG. 12 is as follows. A detailed description of the laminated piezoelectric element 11 will be omitted. When a two-phase alternating voltage is applied to the laminated piezoelectric element 11, an expansion and contraction movement is generated in the laminated piezoelectric element 11, and primary bending natural vibrations in a direction parallel to the plane of FIG. 12 and a direction perpendicular to the plane of FIG. 12 are generated in the vibrating member 1. When the two vibrations are generated with a phase shift in time of 90 degrees, a rightward or a leftward circular motion is generated in the vibrating member 1 around the position of the support bar 5 in case that there is no vibration. The elastic member 9 has a groove 9a for enlarging the vibration displacement, and a swinging motion as indicated by the arrows of FIG. 12 is generated at the forward end of the elastic member 9. As seen from the contact surface (the upper surface of the frictional ring), this vibration corresponds to a 1-wave traveling wave. When the rotor 2 having the contact spring 22 is brought into pressure contact with the vibrating member 1, the rotor 2 comes into contact with the upper surface of the frictional ring 9b with only one portion thereof in the vicinity of the antinode of the traveling wave shifted to the rotor side of the vibrating member 1, and rotates in the direction opposite to the traveling direction of the traveling wave. The rotation output of the rotor 2 is extracted by the gear 4 engaged with the main body 21 of the rotor 2 and the flange 7.
The natural mode of the vibrating member 1 is designed such that the vibration amplitude of the flange 7 is very small, and the main body 21 of the rotor 2 is designed such that its inertial mass is large enough not to allow any vibration to be caused by the excitation of the vibrating member 1. Further, the contact spring 22 of the rotor 2 is designed such that its natural frequency is sufficiently higher than the driving frequency of the vibrating member and that it follows the vibration.
Note that the contact spring 22 of the rotor 2 is formed through heat treatment of stainless steel to achieve an increase in hardness to thereby enhance wear resistance, and there is no fear that edge chipping will occur as in the case of a contact spring formed of anodized aluminium. The frictional ring 9b is harder than the contact spring 22. Since it is mainly the contact spring 22 that is worn, the frictional ring 9b is hardly rutted.
Here, the contact spring 22 of the rotor 2 will be described with reference to the enlarged view of FIG. 13.
The contact spring 22 is composed of a thin-walled spring portion 22a having elasticity mainly in the radial direction, a thin-walled spring portion 22b which is a flange portion connected to the spring portion 22a and having elasticity in the axial direction, and a forward end portion 22c connected to the spring portion 22b. As stated above, the end surface of the forward end portion 22c constituting the surface coming into contact with the frictional ring 9b is polished to enhance its flatness and to be smoothened after attaching the contact spring 22 to the main body 21.
Note that when the contact spring 22 is formed by a press or the like, the end surface of the forward end portion 22c prior to the processing is not flat as shown in FIG. 14, and there is a fluctuation in an axial dimension H. Thus, it is necessary to flatten the end surface of the forward end portion 22c by grinding or rough-polishing and to attain a predetermined axial dimension before performing finish polishing.
In the case of grinding, it is possible to accurately attain the axial dimension H of the forward end portion 22c. However, large burr is generated at the end surface, which leads to a rather long finish polishing time. Further, in the case of rough-polishing, the end surface can be formed neatly. However, due to the small width of the end surface, the polishing is finished in a short time, so that the fluctuation in the axial dimension H is likely to be rather large. Even so, it is not desirable to perform finish polishing from the beginning since, in that case, it would take even longer till a predetermined dimension is achieved.
Thus, there seems to be room for improvement from the viewpoint of processing the forward end portion 22c of the contact spring 22 in a short time and with high accuracy.
In accordance with the present invention, there is provided a vibration wave driving device including: a vibrating member which has an elastic member and an electro-mechanical energy conversion element and which causes vibration when a drive signal is applied to the electro-mechanical energy conversion element, and a moving member contacting the vibrating member and driven by the vibration, where contact portions of the vibrating member and the moving member are formed so that at least one contact portion protrudes toward the other contact portion and that the vibrating member or the moving member having the protruding contact portion has a surface of a part other than the protruding contact portion in the same plane as the end surface of the protruding contact portion.
When the end surface of the contact portion and the surface of the part other than the contact portion, provided in the same plane, are simultaneously polished, it will be easy to restrain fluctuation in the finish dimension attained by polishing.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.